1. Field of the Invention
The present invention concerns lightened vibrating clamps for tree-shaking fruit harvesting machines.
More precisely, it concerns vibrating tongs of the type constituted by two jaws of an elongated shape where at least one of them is mobile and whose closing (gripping) and releasing (opening) movements are obtained by one or several actuating, generally hydraulic, cylinders. A vibrator with counter-rotating weights or with alternating displacement weights is attached to the framework of the clamps enabling the transfer of high frequency vibrations to the clamps.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
Numerous realizations of such vibrating clamps for mechanical fruit harvesting are known.
Vibrating clamps of this kind are for instance described in the following documents: FR-2 799 610 and U.S. Pat. No. 4,903,471. Mounted on vehicles equipped with various devices for controlling and regulating their operation, they allow mechanical fruit harvesting by shaking trees or fruit-bearing bushes such as for instance, walnut trees, almond trees, hazel trees or shrubs, chestnut trees, olive trees, apple trees, plum-trees, Mirabelle trees, cherry trees, coffee-shrubs, pistachio-trees, etc. . . .
Until these last few years, the mechanical harvesting of fruit by means of vibrating clamps took place after the fruit had reached complete ripeness.
In order to improve the quality of the harvested fruit, numerous producers have decided, in recent years, to move up the fruit harvesting dates, so as to be better in phase with the physiological maturity of the fruit. This requires however the utilization of constantly better performing vibrators, taking into account the greater difficulty to detach and drop the fruit, since the forces of abscission of the latter are in effect much greater for harvesting of unripe fruit.
Now, one knows that the vibration force necessary for shaking the trees so as to achieve a complete harvest is very great (several tens of kilowatt). This vibration force is communicated to the tree through the vibrating clamps. The latter is hence submitted to extreme mechanical stresses. On the other hand, to determine the force of vibration to apply in order to generate the vibrations required for obtaining a satisfactory harvest, one must take into account the fact that the weight of the vibrating clamp is to be added to the virtual weight of the tree in motion during the shaking operation on the latter.
To withstand these stresses and to ensure high reliability, the construction of these vibrating clamps is made of resistant and heavy metallic material.
For example the jaws of the vibrating clamps are generally constituted of properly shaped box beams and are composed of an upper plate and a lower plate that are assembled by lateral plates extending from one end to the other of said upper and lower plates and made integral with the latter by welding. The support or supports of the active elements of the vibrating clamp is generally produced according to the same principle.
One drawback of vibrating clamps of this type, which are nevertheless the best performing ones at present, is that they are extremely heavy. As a matter of fact, the heavier the clamp, and the more difficult or even impossible it becomes to work with high frequencies and/or large amplitudes. In addition to that, the high weight of the vibrating clamps constitutes an obstacle to the ability to reach rapid accelerations, which are desirable for ensuring good results.
Another drawback of vibrating clamps of the aforementioned type results from the assembly by welding of the plates constituting in particular their jaws. In fact, it is well known that this process of assembly generates stresses and sometimes incipient cracks in the area assigned to the parts to be assembled. On the other hand, while the vibrating clamps are in operation, the vibrations and stress are very substantial and damage the welds, which crack because of fatigue. Also, the assembly by a welding process of the different parts that need to be rigidly assembled is difficult work requiring the application of safety measures, and the parts assembled in this manner cannot be disassembled, for instance to repair a possible failure of one of them.
Early harvesting requires now the application of greater forces, which are difficult to produce by the tractors or harvesting machines, which have power deliveries and which cannot easily be extended. The tractors and harvesting machines generally are powered by 100 HP combustion engines.
To meet this larger vibration requirement, the only technical solution, with the same power availability, is to reduce the weight of the vibrating clamp. This weight reduction can be obtained by lightening up the various elements of the clamp, knowing that it is not possible to reduce the eccentric weights, which produce the vibrations, because on the contrary, to increase the intensity of the vibrations, it would actually be necessary to increase these weights.
In document FR-2 799 610, a vibrating head has been proposed which features a lightened vibrating clamp each jaw of which consists of two elongated plates made of a material with a high bending yield limit. These plates present the particularity of being obtained by laser cutting and being assembled in superposition and at a distance from each other by means of fastened spacers fastened to the plates by screws.
However, such a vibrating clamp does not present a very significant weight reduction, and hence does not provide a satisfactory solution to the aforementioned problems.
One objective of the present invention is thus to obtain a very substantial reduction of the weight of the vibrating clamps without lessening their capacity to withstand the mechanical stresses of bending, torsion, and shearing, and to stand up to the alternating stresses of fatigue.